I am buying low temperature pasteurized non-homogenized milk for making cheese. It is Jersey milk, and it has a lot of cream in it. I need skim milk for some cheeses that I want to make. I can buy skim milk from the same source, but it costs exactly the same $7 per gallon as the full fat milk. It seems a waste to buy it pre-skimmed for the same price when I could use that cream for butter or Creme Fraiche or ice cream or coffee whenever its not needed for the cheese.

The milk comes in plastic milk jugs, so I can't just ladle the cream off the top. If I pour the milk into my vat, the cream gets mixed in and take too long to rise to the top. So, I thought perhaps I could just pour the milk into a gallon jar with a spigot, put it back in the fridge, let it separate, then drain off the milk from the bottom.

Any problems with that approach? Is there a better way to do it when the milk comes in standard milk jug with the small 1 inch opening? Finally, about how long should it take for the cream to separate from the milk again after pouring it from the milk jug to the glass jar?

Instead of transferring to another container, couldn't you just punch a small hole in the bottom of the original plastic jug to drain the milk out from under the cream layer? The turbulence might stir the cream through a bit, though - depends how dense the cream layer is.

Ah, the opaque bottle might make it tricky - perhaps just drain it into some kind of measuring container and stop when there's only a few cups left? Jersey milk tends to be pretty high fat, there's another thread discussing it - I think they said 2-4 cups cream per gallon is normal (although the term "cream" in this context is going to be pretty variable).

Also, if using this technique remember to loosen/remove the cap before starting to drain, otherwise you'll create a partial vacuum, followed by big "gloops" of incoming air which will stir up the milk.

And if I was using this method for the first time, I'd put both layers into the fridge to settle anyway - just so I could see how well it separated them. But then again, I'm a science geek.

Caseus, when I got my milk in plastic jugs that's how I did it, too - loosen cap, poke a hole in the bottom and let the milk run out. You WILL be able to see the cream as it starts to come out the hole (color change) - at that point I just upended the jug into whatever container the cream was going into. So you don't have to worry too much about being able to see the cream line through the opague jug - just when you think it's getting close, DON'T WALK AWAY!

A mixture of maths & guesswork. I figure that a cream layer with the thickness of "pouring cream" will be around 35% fat, so I will need to skim off 3 cups of cream to remove 1 cup worth of fat. But cream varies - I've seen some Jersey milk which formed a thick cake resembling "double cream", which must've been at least 45-50% fat. So that's the guesswork part.

The specific calculations depend on what your starting fat % & target fat % are, and also what units you're working in. I'm guessing you're trying to get ~5% Jersey milk down to ~2% "skimmed"?

Yes, precisely. I want to make linuxboy's (Pav's) Tomme, which calls for 2% skimmed milk. There is a long thread that discusses this particular recipe. I believe some people use full fat milk, but I'd like to try it they way it is written in this recipe.